The present invention relates to a shaped body, preferably in the form of a flat film, which contains fluorohydrocarbon polymers, which exhibits good long-term thermal stability and which has improved mechanical properties, as compared with shaped bodies known from the state of the art. The present invention also provides for the use of the shaped body in electrical applications.
The known films of fluorohydrocarbon polymers often have long-term thermal stability values which fall within the VDE heat classes B, F or higher. However, if they are to be used as insulating materials, e.g., for motor insulating purposes, they must fulfill further requirements concerning special mechanical properties, such as resistance to penetration, folding strength and stiffness. In films of this type, however, these properties are not present at all, or are present only to an unsatisfactory degree.
It is generally known to improve some of the mechanical properties, in particular the strength and hardness, of shaped bodies made of plastic materials by embedding into them materials in the form of threads, fibers or platelets. However, the effects achieved by this means are very small and insufficient in the case of substantially non-three-dimensional shapes, such as, in particular, films. Besides, most of these additives are of an inorganic nature. They are, e.g., made of glass, carbon, metal, boron, metal oxides, nitrides or silicates, such as asbestos or mica. Additives of this kind are disadvantageous since, at the high temperatures arising during the processing, they are chemically reactive toward polymers containing fluorine, so that a degradation of the polymers results. Furthermore, the reactions can be accompanied by vigorous reactions releasing heat and gas, and therefore they represent a considerable source of hazards in industrial practice. Apart from that, losses in toughness, such as, e.g., a reduced resistance to tear propagation of the shaped bodies, particularly films, formed of fluorohydrocarbon polymers, are observed when such additives are used.
A known means for improving the mechanical properties, especially of films, consists in combining them with other layers having better mechanical properties, e.g., other films; knitted, woven or non-woven fabrics; coatings or, other layers in coextruded materials. However, the considerable technical expense and costs characteristic of this approach are serious disadvantages to its practical use. Apart from that, if good long-term thermal stability is required of the layer components also, then relatively few and, in most cases, rather expensive materials, e.g., the aromatic polyimides, are suitable for this purpose. For the remaining layers, which are not long-term thermally stable, it is difficult to obtain a firm and lasting bonding strength between the fluorohydrocarbon polymers and the above-mentioned layers, due to the extremely abhesive properties of the fluorohydrocarbon polymers. In practice, this becomes apparent by a disturbing tendency of the composites to delaminate.